1. Field of the Invention
The present invention relates to an improved method for the manufacture of sliders for disk drives. More particularly, the invention relates to a method for controllably producing very high crown and camber in the air bearing surface of a slider by applying pulsed laser energy in accordance with the method of the present invention to the back side of the slider in order to induce stress, and thus curvature in the slider material.
2. Description of the Background Art
Magnetic storage disk drives typically include a magnetic sensor called a xe2x80x9cheadxe2x80x9d suspended in close proximity to the magnetic disk, which serves as the recording medium. In Winchester-type disk drives, a magnetic thin film head is embedded in a ceramic block, called a slider, which is then attached to a flexible suspension. During operation, the rotation of the magnetic disk relative to the slider provides an air-flow along the surface of the slider, which causes it to lift, so that the slider is supported on a cushion of air. This surface of the slider is referred to as the Air Bearing Surface (ABS) and its separation from the disk the Fly Height (FH). The shape of the slider and of the ABS in particular is crucial to the performance of the head. Contours in the ABS establish the desired pressure gradients for positioning the slider above the disk surface. It is therefore typically necessary to form complex contours in the shape of the slider by micro-machining, etching, or other processes to obtain the desired performance.
As more is learned about the dynamics of flying heads, more subtle changes are being required in the shape of the ABS. To implement these refinements, it is becoming more and more desirable to create contours which are complex in three dimensions. Two parameters pertaining to the curvature or flatness of the ABS that are considered important are xe2x80x9ccrownxe2x80x9d and xe2x80x9ccamberxe2x80x9d. Crown is the maximum separation of the cylindrical contour along the flying direction from an imaginary plane drawn between the two end edges, i.e., the leading and trailing edges, of the ABS. Camber has a similar definition and is the separation from an imaginary plane drawn between the two side edges of the slider. For the modern xe2x80x9cpicoxe2x80x9d sliders, these curvature parameters are typically on the order of several nanometers (nm), while the slider width and length are about 1 mm. The curvatures of the ABS are therefore truly minute, however, the variance of the crown and camber of modern sliders remains to be a key factor for the slider performance. Hence, there is an obvious need to develop and implement a method to finely adjust crown and camber.
A variety of techniques are currently being practiced for controlling the slider curvature beyond the capability of conventional lapping. All these techniques rely on inducing a surface stress change (xcex94S) on at least one slider surface. This change of surface stress can be (1) positive (i.e., increase of compressive stress) or (2) negative (i.e., decrease of compressive stress). The change in surface stress produces a curvature change in the slider, as shown in FIGS. 1A and 1B. FIG. 1A shows surface layers having residual compressive stresses in the shaded areas. In FIG. 1B, the surface residual stress on the top surface, assumed to be the flex side, (also called the back side) has been reduced by xcex94S, while on the bottom (ABS) side, the residual compressive stress is unchanged. If only one surface is stress-modified by xcex94S, this surface will become more convex or concave if xcex94S is positive or negative, respectively. This effect is easy to visualize if the original surface is exactly flat, as shown in FIG. 1A. In this case, the crown change C (which is the xe2x80x9cbulgingxe2x80x9d of the slider ABS as viewed from the y-direction) is simply given by:
C=[3(1xe2x88x92xcexd)/4E](L/a)2(xcex94Sxc3x97b)
where L is the length of the slider, a is its thickness, b is the depth of the surface stress layer, xcexd is Poisson""s ratio, and E is Young""s modulus. The camber change is also given by a similar equation for the xe2x80x9cbulgingxe2x80x9d of the slider as viewed from the x-direction.
Several techniques for producing positive or negative stress changes on a slider surface are known. Techniques to induce negative stress changes (i.e., reducing the existing compressive stress, or inducing tensile stress on the surface) are usually practiced on the flex side of the slider, in order to produce an increase in the crown or camber at the ABS side. Stress-reducing techniques that can be used at the flex side include xe2x80x9ckiss-lappingxe2x80x9d or plasma etching, which can remove part or all of the stressed layer on the surface. However, such processes have characteristics which detract from their use in a commercial environment.
A more recent approach to slider shaping is the use of laser scribing. Using a laser for creating curvature in sliders is found in U.S. Pat. No. 5,982,583 to Strom. It states in claim 1 the use of a laser to melt and then cool the back surface (here referred to as the flex side) of a slider to add tensile stress which causes tensile stress relief cracks in the back surface, and which causes the air bearing surface to curve thus modifying crown or camber. Strom""s tensile stress relief cracks are oriented predominately parallel to the crown curvature axis. The present inventors regard cracks as undesirable, and should be reduced or minimized in number and size so as not to worsen the surface integrity. The presence of such tensile stress cracks as required by the prior art is an indication that excessive laser power is used to melt excessive amounts of material, and such excessive laser power may damage the sensor which is embedded in the ceramic slider material.
Although some presence of micro-cracks are inevitable when the surface is made xe2x80x9ctensilexe2x80x9d, preferably any cracks made by laser processing should be only very microscopic micro-cracks, visible with a Scanning Electron Microscope. Such micro-cracks tend to orient randomly. An improved approach therefore is to minimize any tensile stress cracks.
Consequently, there is a need for an improved method of laser processing of sliders which does not require the introduction of tensile stress relief cracks in slider material.
It is, therefore, an object of the present invention to provide an improved method for creating controllable crown and camber in sliders by using pulsed laser energy in accordance with the present invention to produce specific, controllable minute curvatures, without the required introduction of tensile stress relief cracks. Other objects and advantages will become apparent from the following disclosure.
The present invention relates to a method and apparatus for producing very high crown and camber curvature in slider materials using a laser processing system which produces fluence, which is variable in a controllable manner, by applying a laser beam to the flex side of the slider material and varying the fluence of the laser beam to form the curvature in the slider material.
A more thorough disclosure of the present invention is presented in the detailed description which follows and the accompanying figures.